The present invention relates to a method of, and circuit for, controlling the discharge of a battery and to equipment operating in accordance with the method, and has particular, but not exclusive, application to portable communication devices, such as radio pagers, and telemetry modules.
For convenience of description the invention will be described with reference to a radio pager. Radio pager circuits are designed for low power consumption to enable a long battery life. In addition, radio pagers operate according to protocols such as CCIR Radiopaging Code No. 1 (also known as POCSAG) which include power saving features which enable the pager to switch off the majority of its circuits for most of the time. For example, the radio receiver in a pager will be active periodically to sample the radio channel for calls, during which time it will consume, for example, 5 mA, and for the remainder of the time it will be off. A radio pager also includes some circuits that consume a higher current, for example an audio alerter will consume about 100 mA and a vibrating alerter will consume about 30 mA, but these circuits are active only infrequently.
Developments in battery technology have resulted in batteries having an increased energy capacity, for example 2 AHr in some new AAA size batteries compared with 1 AHr in conventional AAA batteries. However, in order to derive the full benefit of these new battery technologies, the battery needs to be operated at a relatively high current level due to the chemical energy conversion processes which take place within the battery. Therefore, when such a battery is used in low current applications, the full benefit of the battery""s enhanced energy capacity is not derived and the life of the battery is prematurely shortened.
An object of the present invention is to enhance battery life.
According to one aspect of the present invention there is provided a method of controlling the discharge of electrical energy from a battery into an application circuit, comprising:
a) transferring intermittently energy from the battery to an energy store,
b) transferring energy from the energy store to a voltage regulator, and
c) transferring energy from the voltage regulator to an application circuit,
wherein the peak current flowing from the battery is larger than the peak current flowing into a voltage regulator.
In this way a relatively high pulsed current drawn from the battery is transformed into a relatively low current drawn by the voltage regulator and application circuit.
According to a second aspect of the present invention there is provided a circuit for controlling the discharge of electrical energy from a battery into an application circuit, comprising means for transmitting energy from the battery to an energy store, means for transferring energy from the energy store to a voltage regulator, and means for transferring energy from the voltage regulator to an application circuit; wherein the peak current drawn from the battery is larger than the peak current flowing into the voltage regulator.
In one embodiment of the invention, means are provided to transfer energy periodically from the battery to the energy store. In this way the energy store is maintained in a charged state in readiness for supplying current to the voltage regulator and application circuit.
In another embodiment of the invention, means are provided to enable the transfer of energy from the battery to the energy store when the voltage at the input to the voltage regulator falls below a predetermined level. In this way current is drawn from the battery only when the energy store is depleted by the current drawn by the voltage regulator and application circuit.
If desired, means are provided for measuring the time taken for the voltage at the input to the voltage regulator to change between two predetermined voltage levels and, in response to said time complying with a predetermined criterion, enabling the current drawn from the battery to bypass the energy store.
According to a third aspect of the present invention there is provided a circuit for controlling the discharge of electrical energy from a battery into an application circuit, comprising means for connection to the battery, first switching means coupled to the battery connection means to enable and disable flow of current from the battery, control means for controlling the operation of the first switching means such that the flow of current from the battery is intermittent, an energy store coupled to the first switching means to store energy delivered from the battery, a voltage regulator coupled to the energy store to draw current from the energy store, said current having a lower peak value than the peak value of the current flowing from the battery into the energy store, and means for coupling an output of the voltage regulator to an application circuit whereby current is drawn from the voltage regulator.